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<div class="section">
<div class="titlepage"><div><div><h5 class="title">
<a name="spirit.karma.reference.auxiliary.attr_cast"></a><a class="link" href="attr_cast.html" title="Attribute Transformation Pseudo Generator (attr_cast)">Attribute
          Transformation Pseudo Generator (<code class="computeroutput"><span class="identifier">attr_cast</span></code>)</a>
</h5></div></div></div>
<h6>
<a name="spirit.karma.reference.auxiliary.attr_cast.h0"></a>
            <span class="phrase"><a name="spirit.karma.reference.auxiliary.attr_cast.description"></a></span><a class="link" href="attr_cast.html#spirit.karma.reference.auxiliary.attr_cast.description">Description</a>
          </h6>
<p>
            The <code class="computeroutput"><span class="identifier">attr_cast</span><span class="special">&lt;</span><span class="identifier">Exposed</span><span class="special">,</span>
            <span class="identifier">Transformed</span><span class="special">&gt;()</span></code>
            component invokes the embedded generator while supplying an attribute
            of type <code class="computeroutput"><span class="identifier">Transformed</span></code>.
            The supplied attribute gets created from the original attribute (of type
            <code class="computeroutput"><span class="identifier">Exposed</span></code>) passed to this
            component using the customization point <a class="link" href="../../../advanced/customize/transform.html" title="Transform an Attribute to a Different Type (Qi and Karma)"><code class="computeroutput"><span class="identifier">traits</span><span class="special">::</span><span class="identifier">transform_attribute</span></code></a>.
          </p>
<h6>
<a name="spirit.karma.reference.auxiliary.attr_cast.h1"></a>
            <span class="phrase"><a name="spirit.karma.reference.auxiliary.attr_cast.header"></a></span><a class="link" href="attr_cast.html#spirit.karma.reference.auxiliary.attr_cast.header">Header</a>
          </h6>
<pre class="programlisting"><span class="comment">// forwards to &lt;boost/spirit/home/karma/auxiliary/attr_cast.hpp&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">spirit</span><span class="special">/</span><span class="identifier">include</span><span class="special">/</span><span class="identifier">karma_attr_cast</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
</pre>
<p>
            Also, see <a class="link" href="../../../structure/include.html" title="Include">Include Structure</a>.
          </p>
<h6>
<a name="spirit.karma.reference.auxiliary.attr_cast.h2"></a>
            <span class="phrase"><a name="spirit.karma.reference.auxiliary.attr_cast.namespace"></a></span><a class="link" href="attr_cast.html#spirit.karma.reference.auxiliary.attr_cast.namespace">Namespace</a>
          </h6>
<div class="informaltable"><table class="table">
<colgroup><col></colgroup>
<thead><tr><th>
                    <p>
                      Name
                    </p>
                  </th></tr></thead>
<tbody><tr><td>
                    <p>
                      <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">attr_cast</span> <span class="comment">//
                      alias: boost::spirit::karma::attr_cast</span></code>
                    </p>
                  </td></tr></tbody>
</table></div>
<h6>
<a name="spirit.karma.reference.auxiliary.attr_cast.h3"></a>
            <span class="phrase"><a name="spirit.karma.reference.auxiliary.attr_cast.synopsis"></a></span><a class="link" href="attr_cast.html#spirit.karma.reference.auxiliary.attr_cast.synopsis">Synopsis</a>
          </h6>
<pre class="programlisting"><span class="keyword">template</span> <span class="special">&lt;</span><span class="identifier">Exposed</span><span class="special">,</span> <span class="identifier">Transformed</span><span class="special">&gt;</span>
<span class="special">&lt;</span><span class="identifier">unspecified</span><span class="special">&gt;</span> <span class="identifier">attr_cast</span><span class="special">(&lt;</span><span class="identifier">unspecified</span><span class="special">&gt;);</span>
</pre>
<h6>
<a name="spirit.karma.reference.auxiliary.attr_cast.h4"></a>
            <span class="phrase"><a name="spirit.karma.reference.auxiliary.attr_cast.template_parameters"></a></span><a class="link" href="attr_cast.html#spirit.karma.reference.auxiliary.attr_cast.template_parameters">Template
            parameters</a>
          </h6>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
<col>
</colgroup>
<thead><tr>
<th>
                    <p>
                      Parameter
                    </p>
                  </th>
<th>
                    <p>
                      Description
                    </p>
                  </th>
<th>
                    <p>
                      Default
                    </p>
                  </th>
</tr></thead>
<tbody>
<tr>
<td>
                    <p>
                      <code class="computeroutput"><span class="identifier">Exposed</span></code>
                    </p>
                  </td>
<td>
                    <p>
                      The type of the attribute supplied to the <code class="computeroutput"><span class="identifier">attr_cast</span></code>.
                    </p>
                  </td>
<td>
                    <p>
                      <code class="computeroutput"><span class="identifier">unused_type</span></code>
                    </p>
                  </td>
</tr>
<tr>
<td>
                    <p>
                      <code class="computeroutput"><span class="identifier">Transformed</span></code>
                    </p>
                  </td>
<td>
                    <p>
                      The type of the attribute expected by the embedded generator
                      <code class="computeroutput"><span class="identifier">g</span></code>.
                    </p>
                  </td>
<td>
                    <p>
                      <code class="computeroutput"><span class="identifier">unused_type</span></code>
                    </p>
                  </td>
</tr>
</tbody>
</table></div>
<p>
            The <code class="computeroutput"><span class="identifier">attr_cast</span></code> is a function
            template. It is possible to invoke it using the following schemes:
          </p>
<pre class="programlisting"><span class="identifier">attr_cast</span><span class="special">(</span><span class="identifier">g</span><span class="special">)</span>
<span class="identifier">attr_cast</span><span class="special">&lt;</span><span class="identifier">Exposed</span><span class="special">&gt;(</span><span class="identifier">g</span><span class="special">)</span>
<span class="identifier">attr_cast</span><span class="special">&lt;</span><span class="identifier">Exposed</span><span class="special">,</span> <span class="identifier">Transformed</span><span class="special">&gt;(</span><span class="identifier">g</span><span class="special">)</span>
</pre>
<p>
            depending on which of the attribute types can be deduced properly if
            not explicitly specified.
          </p>
<h6>
<a name="spirit.karma.reference.auxiliary.attr_cast.h5"></a>
            <span class="phrase"><a name="spirit.karma.reference.auxiliary.attr_cast.model_of"></a></span><a class="link" href="attr_cast.html#spirit.karma.reference.auxiliary.attr_cast.model_of">Model of</a>
          </h6>
<div class="blockquote"><blockquote class="blockquote"><p>
              <a class="link" href="../generator_concepts/unarygenerator.html" title="UnaryGenerator"><code class="computeroutput"><span class="identifier">UnaryGenerator</span></code></a>
            </p></blockquote></div>
<div class="variablelist">
<p class="title"><b>Notation</b></p>
<dl class="variablelist">
<dt><span class="term"><code class="computeroutput"><span class="identifier">g</span></code></span></dt>
<dd><p>
                  A generator object.
                </p></dd>
</dl>
</div>
<h6>
<a name="spirit.karma.reference.auxiliary.attr_cast.h6"></a>
            <span class="phrase"><a name="spirit.karma.reference.auxiliary.attr_cast.expression_semantics"></a></span><a class="link" href="attr_cast.html#spirit.karma.reference.auxiliary.attr_cast.expression_semantics">Expression
            Semantics</a>
          </h6>
<p>
            Semantics of an expression is defined only where it differs from, or
            is not defined in <a class="link" href="../generator_concepts/unarygenerator.html" title="UnaryGenerator"><code class="computeroutput"><span class="identifier">UnaryGenerator</span></code></a>.
          </p>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
                    <p>
                      Expression
                    </p>
                  </th>
<th>
                    <p>
                      Semantics
                    </p>
                  </th>
</tr></thead>
<tbody>
<tr>
<td>
                    <p>
                      <code class="computeroutput"><span class="identifier">attr_cast</span><span class="special">(</span><span class="identifier">g</span><span class="special">)</span></code>
                    </p>
                  </td>
<td>
                    <p>
                      Create a component invoking the generator <code class="computeroutput"><span class="identifier">g</span></code>
                      while passing an attribute of the type as normally expected
                      by <code class="computeroutput"><span class="identifier">g</span></code>. The type
                      of the supplied attribute will be transformed to the type
                      <code class="computeroutput"><span class="identifier">g</span></code> exposes as
                      its attribute type (by using the attribute customization point
                      <a class="link" href="../../../advanced/customize/transform.html" title="Transform an Attribute to a Different Type (Qi and Karma)"><code class="computeroutput"><span class="identifier">traits</span><span class="special">::</span><span class="identifier">transform_attribute</span></code></a>).
                      This generator does not fail unless <code class="computeroutput"><span class="identifier">g</span></code>
                      fails.
                    </p>
                  </td>
</tr>
<tr>
<td>
                    <p>
                      <code class="computeroutput"><span class="identifier">attr_cast</span><span class="special">&lt;</span><span class="identifier">Exposed</span><span class="special">&gt;(</span><span class="identifier">g</span><span class="special">)</span></code>
                    </p>
                  </td>
<td>
                    <p>
                      Create a component invoking the generator <code class="computeroutput"><span class="identifier">g</span></code>
                      while passing an attribute of the type as normally expected
                      by <code class="computeroutput"><span class="identifier">g</span></code>. The supplied
                      attribute is expected to be of the type <code class="computeroutput"><span class="identifier">Exposed</span></code>,
                      it will be transformed to the type <code class="computeroutput"><span class="identifier">g</span></code>
                      exposes as its attribute type (using the attribute customization
                      point <a class="link" href="../../../advanced/customize/transform.html" title="Transform an Attribute to a Different Type (Qi and Karma)"><code class="computeroutput"><span class="identifier">traits</span><span class="special">::</span><span class="identifier">transform_attribute</span></code></a>).
                      This generator does not fail unless <code class="computeroutput"><span class="identifier">g</span></code>
                      fails.
                    </p>
                  </td>
</tr>
<tr>
<td>
                    <p>
                      <code class="computeroutput"><span class="identifier">attr_cast</span><span class="special">&lt;</span><span class="identifier">Exposed</span><span class="special">,</span>
                      <span class="identifier">Transformed</span><span class="special">&gt;(</span><span class="identifier">g</span><span class="special">)</span></code>
                    </p>
                  </td>
<td>
                    <p>
                      Create a component invoking the generator <code class="computeroutput"><span class="identifier">g</span></code>
                      while passing an attribute of type <code class="computeroutput"><span class="identifier">Transformed</span></code>.
                      The supplied attribute is expected to be of the type <code class="computeroutput"><span class="identifier">Exposed</span></code>, it will be transformed
                      to the type <code class="computeroutput"><span class="identifier">Transformed</span></code>
                      (using the attribute customization point <a class="link" href="../../../advanced/customize/transform.html" title="Transform an Attribute to a Different Type (Qi and Karma)"><code class="computeroutput"><span class="identifier">traits</span><span class="special">::</span><span class="identifier">transform_attribute</span></code></a>).
                      This generator does not fail unless <code class="computeroutput"><span class="identifier">g</span></code>
                      fails.
                    </p>
                  </td>
</tr>
</tbody>
</table></div>
<h6>
<a name="spirit.karma.reference.auxiliary.attr_cast.h7"></a>
            <span class="phrase"><a name="spirit.karma.reference.auxiliary.attr_cast.attributes"></a></span><a class="link" href="attr_cast.html#spirit.karma.reference.auxiliary.attr_cast.attributes">Attributes</a>
          </h6>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
                    <p>
                      Expression
                    </p>
                  </th>
<th>
                    <p>
                      Attribute
                    </p>
                  </th>
</tr></thead>
<tbody>
<tr>
<td>
                    <p>
                      <code class="computeroutput"><span class="identifier">attr_cast</span><span class="special">(</span><span class="identifier">g</span><span class="special">)</span></code>
                    </p>
                  </td>
<td>
                    <p>
                      <code class="computeroutput"><span class="identifier">g</span><span class="special">:</span>
                      <span class="identifier">A</span> <span class="special">--&gt;</span>
                      <span class="identifier">attr_cast</span><span class="special">(</span><span class="identifier">g</span><span class="special">):</span>
                      <span class="identifier">A</span></code>
                    </p>
                  </td>
</tr>
<tr>
<td>
                    <p>
                      <code class="computeroutput"><span class="identifier">attr_cast</span><span class="special">&lt;</span><span class="identifier">Exposed</span><span class="special">&gt;(</span><span class="identifier">g</span><span class="special">)</span></code>
                    </p>
                  </td>
<td>
                    <p>
                      <code class="computeroutput"><span class="identifier">g</span><span class="special">:</span>
                      <span class="identifier">A</span> <span class="special">--&gt;</span>
                      <span class="identifier">attr_cast</span><span class="special">&lt;</span><span class="identifier">Exposed</span><span class="special">&gt;(</span><span class="identifier">g</span><span class="special">):</span>
                      <span class="identifier">Exposed</span></code>
                    </p>
                  </td>
</tr>
<tr>
<td>
                    <p>
                      <code class="computeroutput"><span class="identifier">attr_cast</span><span class="special">&lt;</span><span class="identifier">Exposed</span><span class="special">,</span>
                      <span class="identifier">Transformed</span><span class="special">&gt;(</span><span class="identifier">g</span><span class="special">)</span></code>
                    </p>
                  </td>
<td>
                    <p>
                      <code class="computeroutput"><span class="identifier">g</span><span class="special">:</span>
                      <span class="identifier">A</span> <span class="special">--&gt;</span>
                      <span class="identifier">attr_cast</span><span class="special">&lt;</span><span class="identifier">Exposed</span><span class="special">,</span>
                      <span class="identifier">Transformed</span><span class="special">&gt;(</span><span class="identifier">g</span><span class="special">):</span>
                      <span class="identifier">Exposed</span></code>
                    </p>
                  </td>
</tr>
</tbody>
</table></div>
<h6>
<a name="spirit.karma.reference.auxiliary.attr_cast.h8"></a>
            <span class="phrase"><a name="spirit.karma.reference.auxiliary.attr_cast.complexity"></a></span><a class="link" href="attr_cast.html#spirit.karma.reference.auxiliary.attr_cast.complexity">Complexity</a>
          </h6>
<div class="blockquote"><blockquote class="blockquote"><p>
              The complexity of this component is fully defined by the complexity
              of the embedded generator <code class="computeroutput"><span class="identifier">g</span></code>.
            </p></blockquote></div>
<h6>
<a name="spirit.karma.reference.auxiliary.attr_cast.h9"></a>
            <span class="phrase"><a name="spirit.karma.reference.auxiliary.attr_cast.example"></a></span><a class="link" href="attr_cast.html#spirit.karma.reference.auxiliary.attr_cast.example">Example</a>
          </h6>
<div class="note"><table border="0" summary="Note">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../images/note.png"></td>
<th align="left">Note</th>
</tr>
<tr><td align="left" valign="top"><p>
              The test harness for the example(s) below is presented in the <a class="link" href="../basics.html#spirit.karma.reference.basics.examples">Basics Examples</a>
              section.
            </p></td></tr>
</table></div>
<p>
            Some includes:
          </p>
<p>
</p>
<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">spirit</span><span class="special">/</span><span class="identifier">include</span><span class="special">/</span><span class="identifier">karma</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">spirit</span><span class="special">/</span><span class="identifier">include</span><span class="special">/</span><span class="identifier">support_utree</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">phoenix</span><span class="special">/</span><span class="identifier">core</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">phoenix</span><span class="special">/</span><span class="keyword">operator</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">fusion</span><span class="special">/</span><span class="identifier">include</span><span class="special">/</span><span class="identifier">std_pair</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">proto</span><span class="special">/</span><span class="identifier">deep_copy</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">iostream</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">string</span><span class="special">&gt;</span>
</pre>
<p>
          </p>
<p>
            Some using declarations:
          </p>
<p>
</p>
<pre class="programlisting"><span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">karma</span><span class="special">::</span><span class="identifier">int_</span><span class="special">;</span>
</pre>
<p>
          </p>
<p>
            The example references data structure <code class="computeroutput"><span class="identifier">int_data</span></code>
            which needs a specialization of the customization point <a class="link" href="../../../advanced/customize/transform.html" title="Transform an Attribute to a Different Type (Qi and Karma)"><code class="computeroutput"><span class="identifier">traits</span><span class="special">::</span><span class="identifier">transform_attribute</span></code></a>:
          </p>
<p>
</p>
<pre class="programlisting"><span class="comment">// this is just a test structure we want to use in place of an int</span>
<span class="keyword">struct</span> <span class="identifier">int_data</span>
<span class="special">{</span>
    <span class="keyword">int</span> <span class="identifier">i</span><span class="special">;</span>
<span class="special">};</span>

<span class="comment">// we provide a custom attribute transformation to allow its use as an int</span>
<span class="keyword">namespace</span> <span class="identifier">boost</span> <span class="special">{</span> <span class="keyword">namespace</span> <span class="identifier">spirit</span> <span class="special">{</span> <span class="keyword">namespace</span> <span class="identifier">traits</span>
<span class="special">{</span>
    <span class="keyword">template</span> <span class="special">&lt;&gt;</span>
    <span class="keyword">struct</span> <span class="identifier">transform_attribute</span><span class="special">&lt;</span><span class="identifier">int_data</span> <span class="keyword">const</span><span class="special">,</span> <span class="keyword">int</span><span class="special">,</span> <span class="identifier">karma</span><span class="special">::</span><span class="identifier">domain</span><span class="special">&gt;</span>
    <span class="special">{</span>
        <span class="keyword">typedef</span> <span class="keyword">int</span> <span class="identifier">type</span><span class="special">;</span>
        <span class="keyword">static</span> <span class="keyword">int</span> <span class="identifier">pre</span><span class="special">(</span><span class="identifier">int_data</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">d</span><span class="special">)</span> <span class="special">{</span> <span class="keyword">return</span> <span class="identifier">d</span><span class="special">.</span><span class="identifier">i</span><span class="special">;</span> <span class="special">}</span>
    <span class="special">};</span>
<span class="special">}}}</span>
</pre>
<p>
          </p>
<p>
            Now we use the <code class="computeroutput"><span class="identifier">attr_cast</span></code>
            pseudo generator to invoke the attribute transformation:
          </p>
<p>
</p>
<pre class="programlisting"><span class="identifier">int_data</span> <span class="identifier">d</span> <span class="special">=</span> <span class="special">{</span> <span class="number">1</span> <span class="special">};</span>
<span class="identifier">test_generator_attr</span><span class="special">(</span><span class="string">"1"</span><span class="special">,</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">karma</span><span class="special">::</span><span class="identifier">attr_cast</span><span class="special">(</span><span class="identifier">int_</span><span class="special">),</span> <span class="identifier">d</span><span class="special">);</span>
</pre>
<p>
          </p>
</div>
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
<td align="left"></td>
<td align="right"><div class="copyright-footer">Copyright © 2001-2011 Joel de Guzman, Hartmut Kaiser<p>
        Distributed under the Boost Software License, Version 1.0. (See accompanying
        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
      </p>
</div></td>
</tr></table>
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